As used herein, the term “stem cell” refers to a cell, which remains undifferentiated into a particular cells type, and, if necessary, has the potential to differentiate into all types of cells constituting the body, including nerve, blood, cartilage, etc. Methods capable of producing such stem cells are broadly classified into two categories: (1) a method of producing stem cells from embryos developed from fertilized eggs (embryonic stem cells); and (2) a method of recovering stem cells stored in each part of the adult human body (adult stem cells). Although embryonic stem cells and adult stem cells are functionally different from each other, they all have the ability to differentiate into various cells types.
The embryonic stem cells have advantages of very good differentiation potential and long telomeres, but have ethical problems and in the disadvantage that they are difficult to obtain in large amounts. In comparison, the adult stem cells can be obtained in large amounts, but have the disadvantage that, when these cells are transplanted into other persons, they carry the risk of infection and have a relatively low differentiation potential.
Despite the above-described disadvantages, adult stem cells are considerably safe for use in medical applications. Specifically, these cells do not cause cancer even when they are transplanted into the body for organ regeneration, and they do not cause immune rejection reactions because they have originated from one's own body. Thus, these adult stem cells can be used for autologous transplantation.
Also, the adult stem cells have site-specific differentiation potential to differentiate according to the characteristics of the peripheral tissues, and do not cause cancer even when they are injected in an undifferentiated state. Thus, these adult stem cells have the potential to produce cells immediately after transplantation and also display the self-renewal potential to create and store undifferentiated stem cells, if necessary.
Due to the above-described advantages, the importance of adult stem cells has recently been highlighted, and various studies have been conducted to obtain adult stem cells in vivo.
Adipose tissue plays an important role in normal growth and physiological action in vivo, but the importance thereof has been previously unappreciated. The most general type of fat is white adipose tissue, which is located below the skin (subcutaneous fat) in the abdominal cavity (visceral fat) or around reproductive organs (gonadal fat). Brown adipose tissue is a slightly less general form of fat present in an adult, which plays an important role in the production of heat during the infant stage (Gimble, New Biol. 2(4): 304-12, (1990)).
However, in fact, reproductive capability and stage of maturity are closely associated with adipose tissue storage in individuals. Female and male adolescence are closely associated with the production and secretion of adipose tissue-derived hormones and with body fat composition. Also, adipose tissue plays an important role in glucose metabolism and energy balance.
For a few years, there has been a significant advancement in the biomaterial field. On the basis of this, many materials are currently developed and used. Despite this progress, many studies have, in fact, not been conducted on the use of human adipose tissue. However, since it was recently reported that adult stem cells are present in adipose tissue (Zuk P A, et al., Molecular Biology of Cell, 13: 4279-4295 (2002); Rodriguez A M, et al., Biochimie, 87: 125-128 (2005)), various studies on the use of adipose-derived cells have been conducted.
Also, with the development of the fields of biochemistry and molecular biology, small amounts of signaling substances (growth factors) have recently been found in the human body, and on the basis of these findings, theories on in vivo aging have been re-established (Stanley Cohen, Nobel Lecture 1986, Dec., 8). Moreover, it has been found that the signaling substances (growth factors) decrease as age increases, and this decrease in the growth factors is closely associated with the aging of the human body (Sporn M and Roberts A, Handbook of Experimental Pharmacology, Vol. 1, Vol. 95/1, 1990, Springer-Verlag, Del., Berlin., pp. 667-698).
Thus, it has been reported that, when external growth factors are administered to the body, the aging of the body can be inhibited, and studies on special effects of these substances have been conducted (GE Pierce and TA Mustoe, Annu Rev Med, 46. 467-481 (1995)). Specifically, studies on the structure and synthesis of the signaling substances (growth factors) have been conducted, but the most of the growth factors have protein structures, which are three-dimensionally complex, thus posing various problems in chemical synthesis and significantly increasing costs for the synthesis.
Accordingly, the present inventors have conducted studies on a method of obtaining active human growth factors at low cost while maintaining the activity thereof in the human body and, as a result, paid attention to the fact that adipose-derived adult stem cells secrete growth factors (Rehman, J. et al., Circulation, 109: 1292-1298 (2004)).
However, studies on adipose-derived adult stem cells mainly relate to the use or differentiation of the cells themselves, and methods of synthesizing growth factors from these cells have not been studied.
Korean Patent Laid-Open Publication No. 2004-94910, entitled “Improved fat cell-differentiated, adipose-derived adult stem cells and the use thereof” discloses a method capable of increasing the in vivo survival rate of adipose-derived adult stem cells, but does not disclose the meaningful synthesis of growth factors. Korean Patent Laid-Open Publication No. 2005-6408, entitled “PBR ligand having function of regulating fat cell differentiation, derivative compounds thereof, and composition for regulation of fat cell differentiation, containing the same”, merely discloses a method of differentiating fat cells into other particular cells.
Also, Korean Patent Laid-Open Publication No. 2005-99274, entitled “Animal serum-free medium composition for culture of human stem cells, and method for induction of differentiation into liver cells”, discloses a method of differentiating human stem cells using animal serum-free medium, and Korean Patent Registration No. 484550, entitled “Method for production of cells for cell transplantation”, discloses the use of stem cells for cell transplantation.
The reason that studies on the synthesis of growth factors using adipose-derived adult stem cells are insufficient is that the methods of using adult stem cells are focused on their use through differentiation into other cells and that studies on the cytological differences between stem cells are insignificant.
Also, as described above, methods for synthesizing growth factors using recombinant genetic techniques have only been studied, as disclosed in Korean Patent Registration No. 101436, entitled “Method for producing recombined human endothelial cell growth factors”, Korean Patent Registration No. 62551, entitled “Method for producing human epithelial cell growth factors by genetic recombination technology”, Korean Patent Laid-Open Publication No. 2003-45032, entitled “Method for producing biologically active human acidic fibroblast growth factors and use thereof for stimulation of angiogenesis”.
Accordingly, the present inventors have discovered a method for producing large amounts of growth factors using adipose-derived adult stem cells and, as a result, found that adipose-derived adult stem cells obtained through the establishment of suitable culture conditions and physical and/or chemical stimulation synthesized and secreted growth factors in significantly effective amounts compared to adipose-derived adult stem cells to which specific stimulation were not applied.
It is an object of the present invention to produce large amounts of human growth factors from adipose-derived adult stem cells, the produced human growth factors having excellent in vivo activity compared to growth factors synthesized by recombinant or chemical methods.
Another object of the present invention is to provide safe and effective drugs or cosmetics containing either human growth factors produced in large amounts from adipose-derived stem cells, or culture media of the growth factors.